1. Field of The Invention
This invention is directed to air conditioning coils and methods of their use.
2. Description of Related Art
Many prior art air conditioning systems require relatively large evaporator coils to achieve higher energy efficiencies. In certain systems it is desired to expose more face area of a coil to an air stream utilizing lower "face velocity," but without enlarging coil height. The "face velocity" of an air conditioning coil is often defined as the total volummetric air flow passing through the coil divided by the total effective upstream side surface area of the coil. For example, the face velocity of a coil having a 2.0 square foot face area across which a 1200 cubic feet/minute air flow occurs would be 600 feet/minute. In various prior art systems refrigerant coils (such as conventional A-coils) used in the indoor sections of air conditioning equipment have a coil face velocity maintained within the 100-500 feet/minute velocity range. A coil face velocity above about 500 feet/minute may result in an unacceptable degree of condensate "blow through" or "blow off" and may raise the air pressure drop across the coil to an undesirable level.
Various prior art coils have two refrigerant coil slabs of a multi-row, multi-circuit construction for purposes of heat exchange efficiency. This multi-row/multi-circuit configuration may result in an air pressure drop across the coil that, as a practical matter, precludes the use in the coil of "enhanced" fins (i.e., fins of, for example, a lanced or louvered construction designed to increase the air-to-fin heat exchange efficiency). Typically fin spacing in prior art coils is between 10 to 22 fins/inch.
FIGS. 1A and 1B show a prior art coil C as disclosed in U.S. Pat. No. 5,207,074 that has a single row/single circuit design with fin spacing in the range of about 16 fins/inch to about 22 fins/inch. Face velocity for such a coil is from about 100 feet/minute to about 200 feet/minute. By "single row/single circuit" is meant that there is a single row R of tubing, typically copper tubing, on each side of each coil and the tubing on each side is a single elongated piece with a plurality of U-turns extending through a plurality of fins F.
FIG. 2 shows another prior art single row/single circuit coil L as disclosed in U.S. Pat. 5,664,431 with single tubing rows T passing through a plurality of fins P. Fin spacing for such a coil may be 16-22 fins/inch and a typical face velocity of 300-450 feet/minute.
FIG. 3 shows prior art coils S, as disclosed in U.S. Pat. No. 5,284,027, each dual row/dual circuit tubing B on each side extending through a plurality of fins N, e.g. with fin spacing of 10-16 fins/inch and a typical face velocity of 170-250 feet/minute.
Another important consideration in coil design for heat pumps is the desire to maintain a certain volummetric relationship between an indoor heat exchanger and an outdoor heat exchanger. Using fewer rows of tubing reduces volummetric capacity and often a receiver is added to maintain the desired relationship (e.g. 0.8:1 to 1.2:1) between an indoor coil and an outdoor coil.
In many prior art coils each side or "slab" of the coil has the same number of rows of tubing and the same fin spacing.
There has long been a need for an effective and efficient air conditioning coil. There has long been a need for such a coil with increased capacity without significantly enlarging coil height. There has long been a need for such a coil with more exposed face area.